1. Field of the Invention
The present invention relates to a capacitive sensor that detects a predetermined physical quantity by detecting an amount of capacitance between a fixed electrode and a movable electrode.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Patent Laid-Open Publication No. 2005-83972 (hereinafter, “Patent Document 1”), there has been known a capacitive sensor that is configured to have a structure such that a movable electrode is supported through an elastic element at a fixing portion by processing a semiconductor substrate with a well-known semiconductor process, so that the movable electrode contacts and separates from the fixed electrode according to an external force applied thereto, and is configured to detect various physical quantities, such as an acceleration rate and an angular speed, by detecting variation in capacitance between these electrodes.
In the capacitive sensor disclosed in Patent Document 1, detecting units to detect capacitance according to variation of a gap between the fixed electrode and the movable electrode are provided at four points in total. Each of the detecting units is structured that the fixed electrode and the movable electrode are opposed to each other in a manner that comb-tooth-shaped portions thereof engage with each other, keeping a predetermined gap therebetween.
However, the capacitive sensor disclosed in the Patent Document 1 is to detect variation in capacitance according to expansion and contraction of the gap between the fixed electrode and the movable electrode (that is, expansion and contraction of the width of a slit between comb-tooth-shaped portions, in the case of Patent Document 1), and if the fixed electrode and the movable electrode shift to be misaligned from each other (that is, to shift in a direction of length of a comb-tooth), the shift changes an area of a region in which the fixed electrode and the movable electrode are opposed to each other, thereby changing capacitance. Such variation of the capacitance leads to a detection error to degrade detection accuracy of the sensor.
It is an object of the present invention to provide a capacitive sensor that is capable of reducing detection errors due to shift of a fixed electrode and a movable electrode.